Recurrent herpes labialis is a common condition and the most common clinical manifestation of herpes simplex virus infection. Although normally self limiting, the disease state is both painful and socially and psychologically debilitating. Serologic studies have indicated that between 50% and 100% of the population have had primary contact with the herpes simplex virus by adulthood. Herpes labialis follows the primary infection usually by a number of years, but only in a proportion of those who had the primary infection. Numerous precipitating factors are recognized as casually related to episodes of herpes labialis including cold weather, sunlight, trauma, stress and menstruation.
Between attacks of herpes labialis, the virus lies dormant in nerve ganglion supplying the affected or symptomatic area. Following reactivation, the virus travels along the nerve to the skin. Once the virus reaches the skin, it replicates and causes an eruption or lesion commonly known as a cold sore.
The development of herpes labialis episodes are well recognized and can be characterized in four stages. The initial stage is a prodromal period lasting for a matter of hours to one to two days. The skin tingles and itches but no cold sore appears. In the next stage ("blister stage"), painful fluid filled blisters appear, which develop at the mucocutaneous junction of the lips. The duration of this stage is variable per individual, but normally lasts about two to five days. In the following stage ("open sore stage"), the blisters rupture and form weeping ulcers. Finally, in the last stage ("scabbed lesion stage"), the blisters dry out and crust over to form a scab. The entire episode with complete resolution of the condition takes seven to fourteen days.
Medical treatment of a herpes labialis episode is currently available. Application of an antiviral agent such as acyclovir heals cold sores. Acyclovir is absorbed through the skin's surface to prevent viral replication. If used at the prodromal (tingle) stage, topical application of acyclovir can prevent the cold sore from appearing.
While the prodromal stage of a herpes labialis episode is characterized by a tingling sensation, recognition of the prodromal stage by this sensation in the symptomatic area is subjective and limited to the individual infected. Further, recognition of the prodromal stage is difficult to quantify. The study of herpes labialis episode has previously been based on subjective clinical parameters such as pruritus and burning. The lack of means to recognize in a large audience, and to quantify repeatedly and accurately the prodromal stage of herpes labialis episode makes it difficult to document case where herpes labialis blisters has been prevented by treatment with antiviral agents such as acyclovir.
It can be understood that if one were to accurately and repeatedly quantify the progress of recurrent herpetic labialis episodes, the prevention of herpes labialis by treatment with an antiviral agent can be documented. What is demanded is a new non-invasive method of assessing the progress of the virus that results in the herpes labialis episodes. Such a technique complements more traditional methods of studying herpes labialis, such as by virus isolation and culture.